Under the LTE (long term evolution) telecommunications standard, Internet Protocol (IP) is the key protocol to transport all services and LTE supports only packet switching with its all-IP (Internet Protocol) network. In an LTE (or LTE Advanced) system, the Evolved Packet Core (EPC) is the latest evolution of the 3GPP core network architecture.
The EPC includes four network elements: Serving Gateway (“SGW”), Packet Data Network Gateway (“PDN GW” or “PGW”), Mobility Management Entity (MME) and Home Subscriber Server (HSS). In an Evolved Packet System (EPS) under LTE, a user equipment (UE) is connected to the EPC over E-UTRAN (LTE access network) which includes Evolved NodeB (“eNodeB”/“eNB”) as the base station for LTE radio signal. The eNodeBs provide E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations toward a user equipment (UE). The eNodeBs are interconnected with each other. A user equipment is connected to the EPC through eNodeBs, and is then connected to external networks through the EPC. Specifically, a UE is connected to an eNodeB(s), eNodeBs are connected to both the MME and the SGW of the EPC, the SGW is logically connected to the PGW, and the PGW is connected to external packet data networks. MME is the key control node in EPC and controls, among others, the selection of PGW(s) for a UE to access external packet data networks. HSS is basically a database that contains user-related and/or subscriber-related information, which may provide support functions in, e.g., mobility management.